1. Field of the Invention
The present invention relates to a liquid crystal display(LCD) device and more particularly, to a backlight assembly and LCD using the same.
2. Description of the Related Art
A cathode ray tube (CRT) is one of the most commonly used display devices. The CRT has been used as a monitor for various electric devices, such as a television (TV), a meter, a computer and an intelligent terminal. Recently, electronic devices have become lighter and smaller to satisfy user demand. However, there are limitations to the size and the weight of an electronic device having the CRT.
To overcome these limitations, several types of display devices have been recently introduced, such as a liquid crystal display (LCD) device using an electric-field optical effect, a plasma display panel (PDP) using gas discharge and an electro luminescence display (ELD) using electro luminescence. Among these recently introduced display devices, the LCD device has often been used as a substitute to CRT because the LCD device has the advantages of being light, thin, and consumes low power.
In general, a liquid crystal display (LCD) device displays an image by controlling amount of light input from an external light source. Therefore, the LCD device requires an additional light source, such as a backlight assembly, to provide light to a liquid crystal display (LCD) panel. Generally, a backlight assembly can be classified as an edge type or a direct type according to the arrangement of the light emitting lamps.
In the edge type backlight assembly, a lamp unit is arranged at an edge of a light guide panel and light emitted from the lamp unit is guided to the light guide panel for generating planar light through the LCD panel. The direct type backlight assembly is used in a large size display device, which is bigger than 20 inches. In the direct type backlight assembly, a plurality of lamps is arranged in rows and the lamps emit light directly to the entire surface of the LCD panel. The direct type backlight unit assembly is mainly used for large sized LCD devices that require high luminance because the direct type backlight unit provides higher light efficiency compared to the edge type backlight assembly.
FIG. 1 is an exploded perspective view of a backlight unit in a direct type liquid crystal display device according to the related art. As shown in FIG. 1, the backlight unit of the direct type liquid crystal display device includes a plurality of lamps 1, a light diffusion unit 11, a first and a second upper supporting units 5 and 5a, a first and a second lower supporting units 4 and 4a, and first and second power terminal units 3 and 3a. 
Each of the first and the second power terminal units 3 and 3a includes a plurality of terminals arranged within a predetermined space. Each of the first and the second power terminal units 3 and 3a is connected to the plurality of lamps 1. External electrodes 2 and 2a are mounted at both ends of the lamps 1 and the external electrodes 2 and 2a are connected to the terminals of the first and the second power terminal unit 3 and 3a. 
The first and the second power terminal units 3 and 3a receive electric power from an inverter and supply the received electric power to the all lamps 1 connected to the first and the second power terminal units 3 and 3a. The first power terminal 3 and the second power terminal 3a are respectively fixed to the first lower supporting unit 4 and the second lower supporting unit 4a, respectively. Also, the first and the second lower supporting units 4 and 4a are fixed to an internal surface of a back cover 10 of the liquid crystal display device. The internal surface of the back cover 10 is coated with a reflector film (not shown) for reflecting light.
The light diffusion unit 11 includes a plurality of diffusion sheets and diffusion plates. The diffusion sheets and diffusion plates are arranged above the lamps for uniformly diffusing the light emitted from the lamps 1.
FIG. 2 is a perspective view showing an external electrode fluorescent lamp (EEFL) that is used as a light source of a direct type liquid crystal display device according to the related art. As shown in FIG. 2, the external electrode fluorescent lamp (EEFL) 40 includes lamp electrode units at both ends of the EEFL 40 like a cold cathode fluorescent lamp (CCFL). The lamp electrode unit (not shown) of the CCFL generally includes an electrode mounted inside ends of a tube, an electrode lead line and a lamp holder for holding the electrode and the electrode lead line. The lamp electrode unit of the EEFL 40 includes external electrodes 43 and 43a externally mounted on both ends of a lamp tube 41 and an insulating layer (not shown) surrounding the external electrodes 43, 43a. 
When a liquid crystal display device is assembled, the external electrodes 43 and 43a of the EEFL 40 are manufactured to be exactly matched with and reside within the upper and the lower supporting units which receive the EEFL 40. Accordingly, the external electrodes 43 and 43a of the EEFL 40 are not exposed.
When a length of the EEFL 40 is shorter than 650 mm, the EEFL 40 emits light with uniform brightness across its entire surface. However, if the length of the EEFL 40 is longer than 650 mm, the EEFL 40 emits light with non-uniform brightness because when the length is longer than 650 mm, the EEFL 40 includes a dim area between two light emitting areas.
FIG. 3A shows uniform light emitting areas and a dim area of an EEFL having a lamp with a 1300 mm length of tube. FIG. 3B is a graph showing a brightness distribution of the EEFL shown in FIG. 3A. To use the EEFL in a large size LCD device bigger than 30 inches, the related art EEFL of a small size LCD device is used by lengthening the lamp tube while maintaining the length of the external electrode. That is, the length of the lamp tube is expanded from 650 mm to 1300 mm. As shown in FIG. 3A, the EEFL with expanded lamp tube includes both emitting areas and a dim area.
Because the external electrode is not lengthened, identical voltage is supplied to the EEFL with expanded lamp tube for emitting light comparing to the same of the related art EEFL. The voltage may be sufficient to uniformly emit light for the related art EEFL which is 650 mm long, but the voltage may be not sufficient for the EEFL having the lengthened lamp tube to uniformly emit light across entire surface of the EEFL. Therefore, in the EEFL with a 1300 mm tube, the dim or non-emitting area is generated. The emitting area and the non-emitting area are simultaneously shown in the graph of FIG. 3B.
As shown in the graph of FIG. 3B, the brightness of a center area of the EEFL is lower than the brightness of edge areas of the EEFL. If high voltage is supplied to the EEFL for overcoming the above mentioned problem, ozone O3 is generated by high voltage supplied to the relatively short external electrode area.
FIG. 4A shows an emitting area and a non-emitting area of an EEFL having lengthened external electrodes and a lengthened lamp tube. FIG. 4B is a graph showing brightness distribution of the EEFL shown in FIG. 4A. As shown in FIG. 4A, the lamp tube and the external electrode are lengthened for using the EEFL of the small size LCD device in the large size LCD device. In the case of lengthening both the lamp tube and the external electrodes of the EEFL, high voltage can be supplied to the EEFL. However, a portion of the lengthened external electrodes occupies the emitting area. Therefore, the non-emitting area becomes wider and the emitting area becomes narrower.
As shown in FIG. 4B, the lengthened EEFL has uniform brightness but the emitting area becomes narrower. More specifically, when the LCD device is assembled, the external electrodes of the EEFL are matched with the upper supporting unit and the lower supporting unit. If the length of the external electrodes becomes longer, the emitting area of the LCD device becomes narrower.